Device for Fixing a Tube for Peristaltic Cassette

ABSTRACT

The invention concerns a peristaltic cassette casing comprising a tube housing forming an arc, characterized in that it comprises tube fixing means arranged along said housing so as to prevent the longitudinal displacement of a tube arranged in said housing.

FIELD OF THE INVENTION

The field of the present invention is that of medical peristaltic systems.

The invention relates more specifically to peristaltic cassettes.

PRIOR ART

A peristaltic cassette system comprises a case containing a housing designed to accommodate rollers and a length of tube.

Operating a peristaltic cassette requires a sufficient compressive force by the rollers on the tube to seal off the volume of liquid between two rollers. This force, combined with the rotation of the rollers about the drive shaft, can cause lengthwise slippage of the tube along the housing inside the case.

This slippage is difficult to control because it is highly dependent on the coefficients of friction between roller and tube, and between tube and case.

This lengthwise slippage of the tube inside the cassette case causes elongation of the tube upstream and in the active part of the cassette, with the following consequences on the performance of the peristaltic cassette:

-   -   A reduction in the compressive force of the rollers causing         premature leaks (due to the reduction in the thickness of the         walls of the tube);     -   A fall-off in the flow rate (due to the reduction in the volume         of the entrance chamber, which in turn is the result of the         reduction in the width of the chamber and its premature closure         by the roller).

Other undesirable effects on the operation of the cassette are also observed, such as an increase in the driving torque, premature tube wear, noise, and stability.

The present invention greatly reduces or even eliminates the abovementioned problems.

The invention is characterized in that the case comprises tube fixing means along the tube housing to prevent longitudinal movement of a tube arranged in said housing. It is also characterized in that the tube fixing means are able to withstand a pressure of more than 2 bar. Having it able to withstand such a pressure considerably limits the traction that the tube could exert on parts of the peristaltic cassette, such as clips.

Other means of fixing the peristaltic tube can be envisaged. Non-restrictive examples that may be cited are adhesive bonding, the use of an injection-molded profiled tube, welding, vulcanization, or fusion of material (e.g. by ultrasound).

The adhesive bonding and use of a profiled tube are described in more detail below by means of the following figures:

FIG. 1 shows an open cassette case before bonding;

FIG. 2 illustrates the different bonding positions;

FIG. 3 shows a profiled tube;

FIG. 4 is a graph showing the flow-rate precision of a conventional cassette in operation;

FIG. 5 is a graph showing the precision of a conventional cassette in operation;

FIG. 6 is a graph showing the precision of flow rate of a cassette in operation with a bonded tube; and

FIG. 7 is a graph showing the pressure of a cassette in operation with a bonded tube.

As can be seen in FIG. 1, the case of the cassette includes five cells around the race defining five locations at which the tube may be bonded to the case. There are five corresponding openings for the introduction of the adhesive.

Bonding is performed in two steps, case closed, with the rollers and the drive shaft keeping the tube in position and held firmly against the case (see FIG. 2).

This bonding also has the effect of securing together the two case halves of the cassette.

Another way of fixing the tube to the cassette case is to give the tube a profile having a longitudinal section, which may or may not be cut, such that it can be gripped and so fixed between the two case halves of the cassette (see FIG. 3).

The invention has been tested on a cassette using adhesive bonding of the tube. An initial series of preliminary tests found a marked improvement in performance as shown by the output flow-rate and pressure curves seen in graphs 1-4.

It goes without saying that the invention is not limited to the abovementioned tube fixing means and that it encompasses any fixing means capable of producing the desired effect. 

1. A peristaltic cassette case comprising a tube housing forming an arc of a circle, said case being characterized in that it comprises tube fixing means along said housing to prevent longitudinal movement of a tube arranged in said housing, said tube fixing means being able to withstand a pressure of more than 2 bar.
 2. The case as claimed in claim 1, characterized in that each fixing means comprises a cavity capable of holding a quantity of adhesive.
 3. The case as claimed in claim 2, characterized in that the cavity forms a depression.
 4. The case as claimed in claim 2, characterized in that the cavity forms a passage connecting the interior and exterior of the housing.
 5. The case as claimed in claim 1, consisting of two case halves, characterized in that at least part of the area of contact of the two case halves is around said housing, said fixing means being formed by the pinching of part of the tube between the two case halves.
 6. A tube for a case as described in claim 5, comprising a longitudinal protuberance designed to be pinched by the two case halves. 